The present invention relates to improvements in a method and in an apparatus for making holes, bores, slits and other forms of perforations or incisions in the walls of tubular bodies, e.g., in the walls of cylindrical commodities which constitute bobbins for storage of textile yarns or the like. More particularly, the invention relates to improvements in a method and apparatus for the making of perforations and/or incisions in the walls of tubular commodities of the type having cylindrical, conical, annular and/or otherwise configurated sections with an axis of rotation. Still more particularly, the invention relates to improvements in a method and apparatus for severing and/or perforating tubular commodities which preferably do, but need not always, consist of a synthetic plastic material, e.g., a synthetic thermoplastic material.
Commonly owned U.S. Pat. No. 4,108,396 granted Aug. 22, 1978 to Adalbert Engel discloses a bobbin which can be used for temporary storage of textile yarns or the like, e.g., for storage of convoluted yarns during contacting of such yarns with a dye. The bobbin is permeable to liquids and, to this end, its wall is formed with numerous holes, slots, bores or like passages for the flow of a fluid from its interior to its exterior and/or vice versa. The bobbin preferably consists of a synthetic thermoplastic material and is preferably deformable in the radial and/or axial direction. The same bobbin can be used with advantage for heat-treatment and/or other treatments of yarns which are convoluted therearound.
It is further known and customary to subdivide an elongated (e.g., continuous) tubular body into shorter sections or discrete commodities by severing the elongated tubular body at regular or irregular intervals in planes which are normal or substantially normal to its axis. For example, such procedure can be resorted to for the mass-production of relatively short or relatively long tubes which are made of cardboard and can serve as cores for convoluted yarns, webs of paper, webs of metallic foil or the like. Analogously, a relatively long elongated tubular body can be subdivided into a succession (e.g., into a single file) of discrete tubes which are used as cores for convoluted sheets of wallpaper or the like. One presently known and often preferred mode of making a continuous tubular body of a synthetic plastic material is blow molding or an analogous technique. Blow molding can involve the making of an endless tubular body or the production of discrete blow molded articles in one or more molds wherein the plastic material is confined from all sides during expansion by air which is blown into the interior of a parison or which is drawn from the mold cavity around the parison. Discrete blow molded articles often require a secondary treatment, for example, cutting away the flash and/or cutting away the bottom wall and/or the top wall so that the finished article is open at one or both axial ends.
It is also known to employ heated needles or like piercing tools for the making of perforations in sheets, foils or the like. This necessitates the use of one or more heaters which consume substantial amounts of energy and contribute to the bulk and initial cost of the perforating apparatus.